The invention relates to a twin scroll exhaust gas turbocharger.
This invention is based on Japanese Published Patent Application JP-A-3-151519. From JP-A-3-151519, a twin scroll exhaust gas turbocharger for a multi-cylinder internal-combustion engine is known. The twin scroll exhaust gas turbocharger has a turbine housing with a first and a second inlet port separated from one another by the turbine housing. The two inlet ports lead into a first and a second spiral duct, respectively, which extend radially on the outside, largely parallel to one another around a rotatably disposed exhaust gas turbine. Exhaust gas from different cylinders of the internal-combustion engine is admitted to both inlet ports corresponding to the ignition sequence of the internal-combustion engine, whereby a more uniform drive of the exhaust gas turbine takes place. The gas inlet ports and the spiral ducts are arranged such that the exhaust gas is guided to the exhaust gas turbines from opposite sides.
The disadvantage of this known embodiment is a high stress to the turbine housing as a result of the temperature, particularly in the area of the spiral ducts.
It is an object of the present invention to avoid the above-mentioned disadvantage.
This and other objects are achieved by a twin scroll exhaust gas turbocharger for an internal-combustion engine, having a turbine housing and having a first and a second gas inlet port separated from one another by the turbine housing, which inlet ports lead into first and second spiral ducts, respectively. The ducts extend radially on the outside around an exhaust gas turbine of the twin scroll exhaust gas turbocharger. The exhaust gas turbine can be rotated about an axis. The gas inlet ports are arranged at least in sections parallel to one another in the turbine housing and radially with respect to the axis of rotation in a mutually spaced manner. The first spiral duct, which connects to the first gas inlet port arranged closer to the axis of rotation, extends up to 180° around the exhaust gas turbine. The second spiral duct, which connects to the second gas inlet port farther away from the axis of rotation, extends up to 180° around the remaining circumference of the exhaust gas turbine.
As a result of the arrangement of the spiral ducts according to the invention on opposite sides of the exhaust gas turbine without any mutual overlapping of the gas flow regions, an overheating of the turbine housing is avoided, particularly in the area of the spiral ducts.
By means of a further development of the invention, the turbine housing has at least one coolant duct between the gas inlet ports through which a coolant can flow. This advantageously reliably avoids an overheating of the turbine housing in the area of the gas inlet ports. Furthermore, as a result of the further development according to the invention, less heat is radiated into the engine compartment, whereby heat protection measures can be reduced, which results in a further cost reduction.
Since an overheating of the turbine housing is reliably avoided as a result of these further developments, in a further particularly preferred embodiment, the turbine housing can be manufactured of a light-metal material, especially aluminum. As a result of this measure, the weight of the exhaust gas turbocharger is advantageously lowered. Furthermore, the manufacturing costs are advantageously reduced because, as a result of the additional cooling, a less expensive turbine housing material can be used.
Advantageously, the sealing problem is also significantly simplified because an easier thermal linking of the exhaust gas turbocharger to the cylinder head or the crankcase becomes possible if the latter are also manufactured of a light-metal material (same or similar thermal expansion coefficient).
In a further development of the invention, a heating element is arrangeable in the coolant. This development is used for heating the turbine housing after a cold start of the internal-combustion engine, whereby the energy lost during the heating of the catalyst is reduced. For heating the heating element, the recuperated energy from the battery of a mild hybrid can, for example, be used.
Definition of a Mild Hybrid: An electric motor, which replaces the conventional starter and generator, starts, and assists the internal-combustion engine. In addition, the potential of the gasoline engine is increased with respect to driving dynamics (boost effect). Simultaneously, consumption advantages of approximately 15% are achieved. The electric motor and the batteries are not designed for driving in a purely electric operating mode.
The heating element, in a particularly preferred embodiment, may be a positive temperature coefficient (PTC) element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.